Not really. I mean you could create a batch file on the MediaAgent and then use the ExecuteProcess to workflow activity to run the batch file. The next challenge then is how you can make the workflow checkl that the restart batch file has worked from the CommServe. I'd imagine that you could create a script to run on the CommServe that does a tcp ping on the MediAgent ports (the script would need to generate a stderr if the tcp ping failed) and retry it every 30 seconds until the tcp ping is alive. Or you could create a batch script to check the state of all the Media Agent services.
Whilst I am sure there are sysadmins with a better programatic eye that what I have, but either way I think it will be a bit clumsy. I guess it needs to be asked, what is the need for the automating the service restart - is it for after hours maintenace or is there a known issue you have that is best resolved through a service restart?